3.0l mercruiser sputters and won’t run under a load.

[Gallen47]

3.0l mercruiser sputters and won’t run under a load.
The boat seems to run ok on muffs.
Changed:
Plugs and wires.
New distributor cap and rotor.
Carb was rebuilt and used spring loaded needle and seat, so I changed that to the solid needle and seat.
Checked timing and tried to run at 2 degrees before and up to 10 degrees before TDC.
Changed the distributor and coil.
Changed the wiring harness on the engine.
It seems that it is not firing on all cylinders but I checked and there is fire.
Thanks for your help.

 

[Bondo]

Ayuh,..... My 1st guess is, it's runnin' Lean,.... Go back to the feul system,....

 

[Fishermark]

...New distributor cap and rotor.

...


Changed the distributor and coil.

What ignition system do you have? Points? Electronic? You mention changing out the distributor. New or used? A little more info will help diagnose the problem.

 

[alldodge]

Agree with Bondo, look into the fuel system. Changed the fuel filter? How is the inside of the carb, is it clean? Fuel pump pressure and flow?

 

[pro-crastinator]

Similar symptoms I had - total frustration.
My OEM Mercury ground wire between coil and block had an internal break in it.
New wire. Everything good.

 

[Gallen47]

UPDATE:
Re-adjusted the valves today, This is an electronic distributor, when I changed it, I put one in that came off a running engine along with the coil. Pulled the number 3 plug wire and there is no difference. For some reason it is not firing on number 3? There is fire on the wire.....this engine ran great when first installed then after a medium left turn it came up missing, Never had this much trouble getting any engine to run. Is there something that could make it miss fire on #3?

 

[Bondo]

UPDATE:
Re-adjusted the valves today, This is an electronic distributor, when I changed it, I put one in that came off a running engine along with the coil. Pulled the number 3 plug wire and there is no difference. For some reason it is not firing on number 3? There is fire on the wire.....this engine ran great when first installed then after a medium left turn it came up missing, Never had this much trouble getting any engine to run. Is there something that could make it miss fire on #3?

Ayuh,.... What's the Compression on #3,..??

 

[Fishermark]

Ayuh,.... What's the Compression on #3,..??

My thought exactly. It could be as simple as a bad spark plug... but I doubt it. Take out the plug and see what it looks like and do a compression check.

 

[Gallen47]

here it is, blown head gasket no compression on 2-3.............

 

[Gallen47]

What could be the cause of the head gasket failure? Can some one recommend sealant for the bolts and head gasket? When I installed the first time I used coppercoat on the gasket and permatex aviation sealant.

I just received the head gasket and it says "no sealant" warranty voided if sealant is used. Is it possible that the coppercoat had an effect the first time?

Thanks for all the help!